Separation of minerals by flotation



Patented Jan. 10, 1933 UNITED STATES ANTOINE MARC GAUDIN, @F BUTTE, EKGNTANA SEPARATION F MINERALS BY FLOTATION Ho Drawing.

My invention relates to improvements in the separation of minerals by flotation, and more specifically relates to the treatment of ores containing sulfides in which the principal base-metal constituents are copper and zinc. One object of my invention is to provide practical means for obtaining improved yields of valuable concentrates in the treatment of ores containing both copper and zinc,

0 and another object of my invention is to provide new and improved means for the flotation treatment of low-grade ores containing minerals separable only with great difficulty r by flotation processes at present known.

There is only one common zinc-bearing sulfide known as sphalerite, ZnS. Sphalerite, however, is sometimes iron-bearing, in which case it is called marmatite, (Zn,Fe)S. @n the other hand copper-bearing sulfides are numerous, and several of these are often found together in one ore. Chalcopyrite @uFeS chalcocite, Cu S, covellite, GuS, bornite (variable, approximately (lu l eS tetrahedrite (approximately Cu Sb S tennantite (approximately Cu As S and enargite (approximately Cu AsS are the commonest. Together with minerals containing copper and zinc, copper-Zinc ores frequently contain pyrite and pyrrhotite which are iron sulfide barren of copper or Zinc and of the nature of undesirable impurities.

In the beneficiation of copper-zinc ores by flotation it is desired to segregate from each other (1) the copper-bearin minerals, (2) the Zinc-bearing minerals, the barren waste and iron sulfides, in order to smelt separately the copper-bearing and zinc-bearing products and to discard the waste.

To date the only copper-Zinc ores that have been treated successfully by selective flotation are those in which the copper occurs as chalcopyrite. Successful treatment of these ores has been obtained by floating the chalcopyrite ahead of the sphalerite or marmatite, then by floating the sphalerite or marmatite ahead of the remainder of the pulp. The usual steps have been as follows:

1. The ore is ground in a circuit made slightly alkaline by the use of lime or soda ash, sometimes in the presence of a cyanide Application filed August 19, 1930. Serial No. 76,455.

or of zinc sulfate or of zinc oxide, or of a combination of these reagents;

2. A mineral collector such as thiocarbanilid, a xanthate or a coal-tar oil, and a frothproducer, such as pine oil or cresylic acid, are added to the pulp just ahead, of, or in the flotation machines, and the copper-bearing froth is'removed in the usual manner;

3. Copper sulfate and lime are added to activate the zinc mineral and inhibit the iron "minerals, respectively. The pulp is conditioned by moderate agitation in a tank;

-l. A mineral collector and a froth producer are added to the pulp just ahead of, or in the flotation machines and the zincbearing froth is removed in the usual manner;

5. Either concentrate may be cleaned by certain combinations of the above steps with or without reg'rinding.

I have found that this customary procedure fails when applied to ores in which the copper occurs partly or wholly in some other form than covellite or chalcopyrite. Modi fication of the customary procedure by substantially changing the alkalinity is of no avail as the zinc mineral floats with the copper minerals in a mixed froth. I have found, however, that a procedure which difiers materially from the customary procedure and which is actually the reverse of such procedure can be put to useful ends in some cases. Specifically, l have discovered that the zincbearing sulfides can be floated ahead of the copper-bearing sulfides if the copper occurs in some other form than covellite or chalcocite. l have also discovered that if the copperbearing material is chalcocite, a substantial modification has to be introduced in the method described above for the treatment of chalcopyritic copper-zinc ores for efiective separation to result. Finally 11 have discovered a complex procedure which is useful in treating ores in which the copper occurs in such combination of forms as to necessitate special treatment.

I have discovered that sphalerite can be floated from a sphalerite-chalcopyrite or a sphalerite-bornite mixture and that the sphalerite of copper-zinc ores is more readily floated than the chalcopyrite or bornite if the circuit is made strongly alkaline or if an oxidizing agent is added or if con-- siderable aeration or conditioning of the pulp is used, or if a combination of these effects is employed. The oxidizing agents that I have found most desirable are bleaching powder, chloride of lime, chlorine, sodium dichromate, potassium permanganate, oxygen and air. Alkaline circuits made 8.1- kaline with lime have shown decided advantages over circuits made alkaline with soda as they have caused a further inhibition of the barren iron sulfides.

In applying my invention to ores containing copper in some other form than chalcopyrite, chalcocite or covellite, I use one of two procedures: I

.1. The zinc-bearing mineral alone is floated from the total pulp, then the copper minerals are floated from the remainder.

2. The copper and zinc-bearing minerals are first floated together from the total pulp. Subsequently they are separated, the zinc mineral floating and the copper minerals being inhibited.

In applying the first procedure the ore may 'be ground with the oxidizing agent, which may be, for example, chloride of lime or chlorine gas, or after grinding the pulp may be stirred in a tank for a suflicient length of time with the oxidizing substance, for example, oxygen. Any combination of these means may also be used. In applying the second procedure the combined copper and zinc minerals may be floated as usual, then separated from each other by the use of oxidizing reagents or of alkaline circuits or of a combination of these following a regrinding or a conditioning treatment or both. When using either procedure a lime circuit is desirable if barren iron sulfides are present in the ore. The inhibiting action of lime on pyrite is well-known and use of it is made in a large number of plants.

In applying my invention to chalcopyrite copper-zinc ores, I prefer, first, to float as much chalcopyrite' as possible away from the remainder of the pulp, as outlined above in Secthe description of the usual procedure.

ondly, I condition the copper concentrate pyrite flotation concentrate containing 17.6% copper and 6.2% zinc was aerated for-fifteen minutes with potassium dichromate, 2.0 lb./tot1, then for ten minutes with lime, 2.0 lb./ton. Flotation was then conducted without the use of other reagents than those already in the concentrate. The concen trate was cleaned once without the use of additional reagents. Metallurgical results were as follows:

Recoverlea% Product Zn Cu grams Zn Cu Rougher tailing 820 0.65 18.8 9.6 83.8 Cleaner concentrate 105 47.50 8.8 80.6 5.3 Cleaner tailing 72 8.2 26.6 9.8 10.9

Example 2.-A synthetic mixture of 84% Product Copper Zine% Cleaner zinc concentrate 50 55.30 Cleaner zinc tailing 5.70 4.40 Cleaner copper concentrate 33.80 32.70 Cleaner cop er tailing 49.20 4.50 Rongher tnl ing v 0.10 0.18 Feed (calculated) 5.00 5.30

Ewample 3.'-A synthetic mixture of 84% pure granite, 8% pure sphalerite and 8% pure enargite was ound in a pebble mill with 1.2 lb./ton lime and 2.0 lb./ton chloride of lime. A rougher zinc concentrate was ob tained on addition of 0.04 lb./ton terpineol and 0.01 lb./ton amyl xanthate; and a rougher copper concentrate on addition of 0.06 lb. /ton terpineol, 0.10 lb./ton amyl xanthate and 0.50 lb./ton sulfuric acid. Metallurgical results were as follows:

Product Copper Zinc Rougher zlnc concentrate 5.30 37.20 Rougher cop er concentrate; 39.50 6.70 Rougller tail ng 0.27 0.20 Feed (calculated) 3.90 5.30

Copper-zinc ores in which chalcocite is the copper mineral do not respond'to the usual treatment given to chalcopyrite-sphalerite ores. In this instance, again, I have found that no satisfactory separation results from the use of the customary procedure. However, I have discovered some peculiarities in the action of cyanides on chalcocite which allow a modification of the customary method so as to obtain positive results.

It is known that cyanides inhibit the naturally activated sphalerite of many of the complex ores by dissolving the film of copper sulfide at its surface; this inhibition is permanent unless copper ions are allowed to reactivate the sphalerite. I have found that cyanides inhibit chalcocite but that this action, in contradistinction to the action of cyanides on sphalerite is not permanent, the chalcocite floating again after immersion in cyanide for a sufficient time. I believe that this is due to the consumption of cyanide by the copper mineral. I have discovered that the metals in mixtures of chalcocite and sphalerite and of copper-zinc ores in which chalcocite is the copper mineral can be segregated by selective flotation if a relatively very high quantity of cyanide is added to the pulp at a high alkalinity (over pH 10) and in the presence of a powerful collector for copper such as amyl xanthate, butyl xanthate, amyl mercaptan or benzyl mercaptan. Use of this combination of reagents results in flotation of the chalcocite but inhibition of the sphalerite. The interpretation that I place on my invention is that no flotation of either mineral takes place as long as there is a substantial concentration of free cyanide ion in the pulp, but that as soon as that concentration is reduced below a certain unknown but very small value,

' the collecting agent comes into play, reacting with the surface of the chalcocite or of some oxidation product thereon, thereby causing the mineral to adhere to air bubbles and report in the froth. If the pH is below 10 the cupric ion concentration seems to be sufficient to activate the sphalerite so that its rejection is unsatisfactory; if the pH is over 13, the chalcocite is difiicult to collect. I prefer therefore to carry out the operation between the limits of pH 10 and 13. The quantity of cyanide added is variable, depending upon the relative quantities of the minerals and the fineness to which they have been ground. In

' general, however, this quantity is much larger than is generally employed for lead-zinc, copper-iron or chalcopyrite-sphalerite selective flotation operations. The quantity of cyanide should be suflicient to inhibit momentarily both the chalcocite and the sphalerite. One to four pounds is the average quantity of cyanide required per ton of mixed chalcocite-sphalerite concentrate.

In applying this invention I prefer, first, to float collectively the chalcoeite with the sphalerite. To this end I use a relatively small amount of a strong collector as mentioned above. This collective concentrate I then treat with an alkali and a relatively large quantity of cyanide to substantially complete inhibition of both chalcocite and sphalerite. The next step is to aerate the pulp in flotation cells. This aeration results in slow flotation of the 'chalcocite in preference to the sphalerite. The following example illustrates the application of this invention.

E wample 4.A synthetic mixture consisting of 84% pure granite, 8% pure chalcocite and 8% pure sphalerite was ground in a pebble mill with 2.0 lb./ton soda ash, then floated with 0.04 lb. /ton terpineol and 0.05 lb. /ton amyl xanthate. The tailing was discarded,'the concentrate cleaned once with no additional reagents then cleaned a second time with 3.0 lb. /ton sodium cyanide for selection ofthe copper from the zinc. Metallurgical results were as follows:

Product Copper Zinc Copper concentrate 67.60 6.70 Zinc concentrate 9. 20 56.30 Cleaner tailing.- 2. 40 3. 00 Rougher tailing 0. 12 0.17

Copper-zinc ores in which copper occurs jointly as covellite, chalcocite, chalcopyrite and as bornite, enargite, tetrahedrite or tennantite can be beneficiated by a combination of the schemes that I have just described. Preferably I proceed as follows, although some modifications of this method which should be obvious from the foregoing can also be used:

1. I float the copper and zinc minerals as a collective concentrate.

2. I condition the collective concentrate with an oxidizing agent and float again. The concentrate consists essentially of chalcocite, covellite and sphalerite, and the tailing of the other copper minerals together with most of the pyrite that had floated in step 1. The tailing is a finished copper product in so far as copper-zinc separation is concerned, but its grade might be raised by subsequent treatment to float the copper minerals away from the impurities in it, particularly pyrite and non-sulfide gangueconstituents.

3. .1 subject the chalcocite-covellite-sphalerite concentrate to a flotation operation after adding considerable cyanide and after bringing the pH in the range of 10 to 13. This results in flotation of the vchalcocite and rejection of the sphalerite, yielding an additional copper concentrate and a zinc concentrate.

The following example illustrates the application of my process to an ore of the Butte district.

E wample 5.The ore consisting essentially of chalcocite, bornite, sphalerite, pyrite and granitic gangue minerals wasground in a pebble mill for one hour with 0.2 lb./ton cyanide and 1.0 lb./ton lime. Flotation was accomplished by the addition of 0.02 lb./ton pine oil and 0.04 lb./ton amyl xanthate. The

- etc.

2. The flotation process which comprises -pH of the pulp was 11.9. The rougher concentrate was conditioned for one hour with 2.5 lb. /ton chloride of lime and then cleaned by flotation without additional reagents. This yielded a sphalerite-chalcocite concentrate. The addition of 0.04 lb./ton amyl xanthate resulted in the production of a copper concentrate consisting essentially of bornite and of pyrite,- and left a cleaner tailing consisting essentially of gangue and pyrite. The pH of the cleaner tailing pulp was 12.1. The chalcocite-sphalerite concentrate was aerated in the flotation cell with approximately 5 pounds cyanide, per ton of chalcocite-sphalerite concentrate. This segregated that product into a chalcocite reclean er concentrate and a sphalerite recleaner tailing. Metallurgical results were as follows:

Metal content Recoveries Product m Cu Zn Fe Cu Zn Fe Chalcoclte concentrate 73 46.30 24.60 2.80 22.80 10.50 0.40 Sphalerlte concentrate m 2.10 54.20 7.20 3.10 70.50 3.40 Bornite concentrate 281 34.80 7.80 18.10 67.10 12.80 15.90 Cleaner tailing 216 2.50 1.60 28.70 3:70 2.00 19.10 Rougher ta1llng 3170 0.16 0.20 6.40 3.30 4.20 61.20 Feed (calculated) 4000 3.70 4.30 &10

Many modifications may be made without departing from the principles of my invention as herein disclosed, and accordingly no oxygen, atmospheric air, or any oxidizing agent equivalent in action to any of the substances named. By coliper sulfide mineral, as used in the claims 0 this application is meant any mineral comprisin copper and sulfur in chemical combinatlon, with or without the presence of iron or other element, the term copper sulfide mineral thus including chalcopyrite, chalcocite, covellite, bornite, tetrahedrite, tennantite, enargite,

hibiting both chalcocite-and sphalerite, treating the pulp with an oxidizing agent and collectively floating chalcocite and sphalerite, refloating with sufficient cyanide to substantially inhibit both chalcocite and sphalerite, treating the pulp with an oxidizing agentand thereafter separating chalcocite from the pulp.

3. The flotation process which comprises separating chalcocite and sphalerite from gangue minerals by collectively floating the chalcocite and sphalerite, treating the concentrate with suflicient cyanide to inhibit both the chalcocite and sphalerite and there,- after aerating the pulp until the inhibiting action of the cyanide upon the chalcocite is substantialy reduced, and thereafter separating chalcocite from sphalerite by flotation.

4. In the separation of minerals by flotation, the process which comprises subjecting to a flotation treatment a mixture comprising chalcocite, bornite, sphalerite and pyrite in an alkaline circuit, conditioning the concentrate with chloride of lime, refloating to separate a concentrate of chalcocite and sphalerite, aerating the concentrate until inhibitory factors) are reduced and then floating to separate the chalcocite from sphalerite.

5. In the separation of minerals by flotation, the process which comprises subjecting a mixture comprising chalcocite, bornite, sphalerite and pyrite to a flotation treatment in an alkaline circuit, separating a primary concentrate of chalcocite and sphalerite and a secondary concentrate of bornite and pyrite, and aerating the concentrate until inhibitory factors are reduced and then floating to separate the chalcocite from sphalerite.

In testimony whereof, I have hereunto subscribed my name this 21st day of Jul 1930. ANTOINE MARC GA DIN.

thereafterv separating chalcocite from. the 

